The KRAS, NRAS and HRAS genes encode a set of closely related small GTPase proteins KRas, NRas and HRas, collectively referred to herein as the Ras proteins or Ras, that share 82-90% overall sequence identity. The Ras proteins are critical components of signalling pathways transmitting signals from cell-surface receptors to regulate cellular proliferation, survival and differentiation. Ras functions as a molecular switch cycling between an inactive GDP-bound state and an active GTP-bound state. The GDP/GTP cycle of Ras is tightly regulated in cells by guanine nucleotide exchange factors (GEFs) such as Sos1 and Sos2, which promote the exchange of GDP for GTP, and GTPase activating proteins (GAPs) such as NF-1 and p120RasGAP which stimulate the intrinsic GTPase activity of Ras hydrolysing GTP to GDP.
The Ras proteins are 188-189 amino acids in length and have a highly conserved N-terminal G-domain containing the p-loop region, which binds nucleotide, and the switch I and switch II regions which are important for regulatory and effector protein interactions. The C-terminal region of the Ras proteins are more divergent and contain elements which regulate the association of Ras with the membrane including the conserved carboxyl terminal CAXX box motif which is necessary for post-translational prenylation modifications. On binding to GTP the switch I and switch II regions of Ras undergo a conformational change which enables its interaction and activation of effector proteins to regulate down-stream signalling pathways. The best characterised effector of Ras is the serine/threonine kinase Raf which regulates the activity of the mitogen-activate protein kinase (MAPK) pathway. The PI3K pathway is another important effector pathway down-stream of Ras with the p110 catalytic subunit of the class I phosphoinositide 3-kinases interacting with Ras. Other effectors of Ras including RalGDS, Tiam1, PLC-ε and Rassf1 have been have also been described (Cox, et al. Nature Reviews Drug Discovery, 2014, 13:828-851).
RAS mutations are frequently found in cancer and approximately 30% of all human cancers have a mutation in KRAS, NRAS or HRAS genes. Oncogenic Ras is typically, but not exclusively, associated with mutations at glycine 12, glycine 13 or glutamine 61 of Ras. These residues are located at the active site of Ras and mutations impair intrinsic and/or GAP-catalysed GTPase activity favouring the formation of GTP bound Ras and aberrant activation of down-stream effector pathways. KRAS is the most frequently mutated RAS gene in cancer followed by NRAS and then HRAS. There are several tumour types that exhibit a high frequency of activating mutations in KRAS including pancreatic (˜90% prevalence), colorectal (˜40% prevalence) and non-small cell lung cancer (˜30% prevalence). KRAS mutations are also found in other cancer types including multiple myeloma, uterine cancer, bile duct cancer, stomach cancer, bladder cancer, diffuse large B cell lymphoma, rhabdomyosarcoma, cutaneous squamous cell carcinoma, cervical cancer, testicular germ cell cancer and others.
Glycine to cysteine mutations at residue 12 of Ras (the G12C mutation) is generated from a G.C to T.A base transversion at codon 12, a mutation commonly found in RAS genes that accounts for 14% of all KRAS, 2% of all NRAS and 2% of all HRAS mutations across cancer types. The G12C mutation is particularly enriched in KRAS mutant non-small cell lung cancer with approximately half carrying this mutation, which has been associated with the DNA adducts formed by tobacco smoke. The G12C mutation is not exclusively associated with lung cancer and is found in other RAS mutant cancer types including 8% of all KRAS mutant colorectal cancer.
To date there have been no inhibitors of G12C mutant Ras proteins which have been approved for therapeutic use. Hence there is a need for new inhibitors of G12C mutant Ras proteins that possess the required pharmaceutical properties to be suitable for clinical use. The compounds of the specification have been found to possess anti-tumour activity, being useful in inhibiting the uncontrolled cellular proliferation which arises from malignant disease. The compounds of the specification provide an anti-tumour effect by, as a minimum, acting as inhibitors of G12C mutant Ras proteins.